There are presently two basic types of commerically available vehicle brake systems. The drum brake is one, and the disc brake the other. Although the disc brake is superior to the drum brake in many respects, the disc brake does not enjoy its expected success for the larger road vehicles such as trucks, tractor-trailers, and the like. For these types of vehicles, there is much room for improvement of commercially available disc brake systems.
In available disc brake systems, the brake pads, or shoes, are quite limited in their contact area. This is of course a significant drawback when one considers the substantial inertial forces which need to be overcome when braking a large road vehicle such as a tractor-trailer. Accordingly, the drum brake is most commonly found in the larger road vehicles.
Attempts have been made, at least in the patent art, to develop disc brake systems having large contact-area brake shoes. Complex brake shoe actuating mechanisms have been proposed in an attempt to develop uniform braking forces over the entire contact surfaces of the shoes. And the problems involved in eliminating the substantial heat developed in this type of braking disc have been recognized. See U.S. Pat. No. 2,535,763 issued to Tucker, U.S. Pat. No. 3,830,345 of Boyles, and the Baxendale U.S. Pat. No. 3,896,907.
In the Tucker patent, there is disclosed a disc brake assembly wherein a unitary brake shoe is controlled by hydraulic fluid flowing into and out of a rubber-like channel member. The disc is segmented, to enable a degree of yield intended to improve contact with the brake shoe. The dissipation of heat is attempted by radial holes extending through the braking disc.
The Boyles braking system is pneumatically or hydraulically actuated, through the means of two expanding tubes intended to control the movement of braking discs positioned on respective sides of a double-faced brake lining structure. The discs are actuated through annular pistons, with fluid being fed to the respective tubes from opposite sides of the assembly. Boyles dissipates heat by specific spacings of elements and the provision of cooling ribs.
In the Baxendale patent, brake actuation is through the means of four hydraulic pistons fed from the same side of the assembly to actuate two annular brake shoes. Cooling is designed to take place by cooling slots which extend into the disc.
As far as is known to the applicant, none of the three disc brake assemblies described above has found its way into the commercial marketplace. This is perhaps because of ineffectual disc cooling, even in the case of the Tucker system with its relatively limited contact areas. Or perhaps absence from the marketplace is due to the complexity of the brake actuating mechanisms, or the inability of the mechanisms to maintain uniform braking forces over the entire disc surfaces. And coupled with the degree of complexity, are factors such as elevated initial cost, difficulty of manufacture, and increased maintenance and repair considerations.
There are no commercially available disc brake systems known to the applicant which utilize large contact-area annular brake shoes, which accomplish efficient cooling, and which nonetheless enjoy simplicity and low cost of construction, maintenance and repair. It is toward the elimination of this deficiency that the present invention is directed.